An mRNA-lipid nanoparticle vaccine against H5N1 influenza virus protects lactating dairy cows from infection.

An mRNA-lipid nanoparticle vaccine encoding H5N1 hemagglutinin protects lactating dairy cows by reducing peak milk viral RNA ~1,000-fold after intramammary challenge.

• Why it matters: HPAI clade 2.3.4.4b H5N1 has emerged in US dairy cattle, with replication in mammary tissue and transmission linked to viral shedding in milk, driving mastitis and milk loss.
• What they did: Eight lactating dairy cows received two intramuscular mRNA-LNP doses encoding HA from A/dairy cattle/Texas/24-008749-002/2024 or saline, then underwent intramammary viral challenge.
• The result: Vaccination induced HA-reactive and neutralizing serum antibodies and HA-reactive milk antibodies, and after challenge it lowered peak milk viral RNA by ~1,000-fold and reduced mastitis and mammary fibrosis occurrence.